The present invention relates to a magnetoresitance effect film and a spin valve reproducing head.
In spin valve reproducing heads of a hard disk drive unit, high reproducing power, narrow core width and stable reproduction are required.
Conventional spin valve reproducing heads are shown in FIGS. 11–13.
A basic spin valve reproducing head called an abutted type head is shown in FIG. 11. The abutted type head includes: a magnetic sensing section 11 which is made of a spin valve film and whose width is equal to that of a track of a recording medium; biasing sections 13 which are made of hard magnetic layers so as to stably magnetize a free magnetic layer 12; and terminal sections 14 for supplying a sensing electric current to the magnetic sensing section 11. The biasing sections 13 are provided on the both sides of the magnetic sensing section 11, and they are magnetized, for example, rightward in the drawing. Magnetic fields leaked from the biasing sections 13 are applied to the magnetic sensing section 11 as biasing magnetic fields. The free magnetic layer 12 of the magnetic sensing section 11 is made of, for example, a soft magnetic layer whose magnetic coercive force is 50 e or less, and it is magnetized rightward in the drawing by the magnetic fields leaked from the biasing sections 13 or the hard magnetic layers. Therefore, even if no magnetic field is given from the recording medium, the free magnetic layer 12 can be magnetized in one direction. With this structure, variation of base lines of reproducing signals can be limited, and the signals can be stably reproduced.
These days, the width of the magnetic sensing section 11 is made narrower. In the case of the magnetic sensing section 11 whose width is 1 μm or less, it is difficult to stably reproduce signals due to unstable zones “A”. Since the unstable zones “A” are separated away from the hard magnetic layers 13, the biasing magnetic fields are smaller than that of dead zones “B”, in which the hard magnetic layers 13 are connected, and the unstable zones “A” cannot be completely magnetized in one direction. If the unstable zones “A” is diagonally magnetized with respect to the biasing magnetic fields, base lines of reproducing signals are varied, so that the signals cannot be stably reproduced.
FIG. 12 shows a terminal-overlay type head, and FIG. 13 shows an exchange bias type head. They have been developed to overcome the disadvantage of the abutted type head.
In the terminal-overlay head shown in FIG. 12, terminal sections 14, which supply a sensing current, overlay the unstable zones “A”. With this structure, the sensing current runs between the terminal sections 14 only. Therefore, no current passes through the unstable zones “A”. The zones, through which no sensing current passes, do not badly influence reproduction voltage, so that the unstable zones can be removed.
However, the terminal-overlay type head has a following disadvantage.
Namely, if width of the unstable zone “A” is, for example, 0.05 μm, preferable width of an overlaying part is 0.05 μm. But it is difficult to make such the narrow overlaying part without deviation by a conventional manner. Especially, if width of the sensing section 11 is 0.5 μm or less, it is highly difficult to make the head.
On the other hand, in the exchange bias type head, a biasing section 15, which is made of an antiferromagnetic film generating a switched connection, covers an end part of the free magnetic layer 12 without the hard magnetic layer 13 as shown in FIG. 13. A switched connection magnetic field directly magnetizes the free magnetic layer 12 in one direction, so that stable magnetizing can be executed. Unlike the abutted type head and the terminal-overlay head, the switched connection magnetic field is not influenced by a distance from the biasing section 15. Therefore, a great bias magnetic field is applied to a zone connected to the antiferromagnetic film 15, and the unstable zones can be removed, so that the free magnetic layer 12 can be stably magnetized.
A process of manufacturing the exchange bias type head will be explained with reference to FIGS. 1–8.
Firstly, a spin valve film 20 is formed (see FIG. 1), and a resist pattern 21 is formed on the spin valve film 20 by photolithography (see FIG. 2).
The spin valve film 20 is ion-milled or ion-etched with the resist pattern 21, which acts as a mask, so as to form into a trapezoid (see FIG. 3). The resist pattern 21 is once removed (see FIG. 4), and another resist pattern 22, whose width is defined by the width of the sensing section and narrower than that of the resist pattern 21 shown in FIG. 2, is formed by photolithography (see FIG. 5). Next, the spin valve film 20 is ion-milled to remove useless substances thereon. The antiferromagnetic film 15 is formed by sputtering (see FIG. 7), and the resist pattern 22 is removed (see FIG. 8).
The above described process is almost equal to a process of manufacturing the terminal-overlay type head.
Unlike the terminal-overlay type head, the free magnetic layer 12 of the exchange bias type head can be stably magnetized. However, the superior exchange bias type head has never been used as a reproducing head. The reason is that intensity of the switched connection magnetic field between the antiferromagnetic film 15 and the free magnetic layer 12 is low so that a sufficient bias magnetic field cannot be applied to the free magnetic layer 12. The inventor thinks that if the ion milling for removing the useless substances (see FIG. 6) is insufficient, a sufficient bias magnetic field cannot be applied to the free magnetic layer 12.
Metal tantalum (Ta) has been used as a surface protection layer for protecting the spin valve film 20. The reasons are: tantalum and tantalum oxides are highly chemically stable; and their resistivity (ρ) is high, e.g., 180 μΩm, so spin valve characteristics are not influenced even if thickness of the film is slightly varied.
However, in the step of manufacturing the exchange bias type head shown in FIG. 6, useless substances in the connecting part are removed by ion milling. In the step, if the protection layer for protecting the spin valve film 20 includes tantalum, the free magnetic layer 12, whose sputtering rate is 1.2–1.5, is partially sputter-removed before tantalum, whose sputtering rate is 0.62, is completely removed. Therefore, magnetic characteristics of the free magnetic layer 12 must be worse, and the intensity of the switched connection magnetic field must be lower. Further, if tantalum is partially left as residue, the switched connection between the antiferromagnetic film 15 and the free magnetic layer 12 must be weak.